Unihedron SQM-LU, SQM-LU-DL-V Operator's Manual

SQM-LU Operator’s Manual

Version: 20170728

List of Figures

2.1 Mpsas interpretive scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.2 Mpsas vs NELM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.1 Front of unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.2 Back of unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5.1 Wired connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

7.1 Splash screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

7.2 File menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

7.3 File Open dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7.4 View menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

7.5 View : Log . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

7.6 View:Directories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

7.7 Data logging header . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

7.8 Set Location dialog . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

7.9 Tool : old log to dat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

7.10 Tool : dat to Moon csv . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

7.11 Tool : Comm terminal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7.12 Help menu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7.13 Help : About . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

7.14 Found device (single) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

7.15 Found device (multiple) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

7.16 USB connection details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

7.17 Ethernet connection details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

7.18 RS232 connection details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.19 Information tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

7.20 Log Continuously screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

7.21 Log Continuously Trigger tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

7.22 Log Continuously Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.23 Log Continuously Annotation tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7.24 Log Continuously GPS tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

7.25 Calibration tab (initial) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

7.26 Calibration tab (populated) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

7.27 Report interval tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

7.28 Firmware tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

7.29 Firmware selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

7.30 Conﬁguration tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

7.31 Light calibration conﬁrmation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

7.32 Dark calibration conﬁrmation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

7.33 Sensor arrangement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

7.34 Fig:Simulation tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

7.35 Accessories tab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

9.1 Housing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

9.2 Example cover calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

List of Tables

2.1 Apparent Magnitudes of Known Celestial Objects adapted from [2] . . . . . . . . . . . . . . . . . . . . . . 10

7.2 simin.csv ﬁeld description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

7.3 Log continuous command line parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

7.4 Select device command line parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

7.5 Select device command line parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

8.1 Summary of standard commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

8.2 Reading request response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

8.3 Unaveraged reading request response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

8.4 Unit information request response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

8.5 Calibration information request response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

8.6 Light calibration response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

8.7 Dark calibration response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

8.8 Disarm calibration response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

8.9 Response for manual setting of light calibration oﬀset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

8.10 Response for manually setting of light calibration temperature . . . . . . . . . . . . . . . . . . . . . . . . 45

8.11 Response of manually setting dark calibration time period . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

8.12 Response for manually setting of dark calibration temperature . . . . . . . . . . . . . . . . . . . . . . . . 46

8.13 Humidity/temperature command summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

8.14 Humidity/temperature response summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

8.15 Display accessory command summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

8.16 Display accessory response summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

8.17 LED accessory command summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

8.18 LED accessory response summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

8.19 Relay accessory command summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

8.20 Relay accessory response summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

8.21 Summary of standard commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

8.22 Continuous reporting command summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

8.23 Response of all continuous reporting requests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

8.24 Interval report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

8.25 Response of viewing or setting interval reporting parameters . . . . . . . . . . . . . . . . . . . . . . . . . . 54

8.26 Response of request for internal simulation values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

8.27 Request simulation (S....x) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

8.28 Response of setting simulation values (S...x) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

13.1 Reading seem too bright . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

13.2 Reading is 0.00mpsas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

13.3 Cannot Find UDM software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

13.4 Driver not found . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

13.5 USB device not found, or more than one device on the same COM port . . . . . . . . . . . . . . . . . . . 62

13.6 Recording stops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

13.7 Meter cannot be found by PC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

13.8 Meter cannot be found by Windows operating system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

13.9 Cannot get a reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

14.1 Glossary of terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

List of Equations

2.1 MPSAS to cd/m2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.2 NELM to MPSAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.3 MPSAS to NELM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

8.1 Raw Temperature to degC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

8.2 degC to Raw Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

1 Introduction

Thank you for purchasing the SQM-LU. You will soon be on your way to collecting scientiﬁc data.

The SQM series of products have been used in the following applications:

• Quantitatively comparing the sky brightness at diﬀerent astronomical observing sites.

• Documenting the evolution of light pollution.

• Setting planetarium dome illumination to mimic the skies that people are likely to experience elsewhere in the city.

• Monitoring sky brightness through the night, night-to-night, and year-to-year for astronomical observation records.

• Determining which nights show the greatest promise for ﬁnding the ’faintest fuzzies’.

• Calibrating the eﬀect of sky brightness on qualitative measures such as the Bortle Scale or NELM.

• Investigating how sky brightness correlates with the solar cycle and month-to-month sunspot activity.

• Helping to provide local ground truth for future sky brightness prediction with the Clear Sky Clock.

• Helping CCD users make a correlation between the SQM reading and when the background reaches some ADC

level.

• Assisting Sea Turtle researchers in studying the amounts of light in areas where turtle hatchlings are aﬀected by artiﬁcial lights.

• Researching bird-song synchronization with dawn.

• Researching twilight brightness changes with the addition of external Neutral Density ﬁlters. Unihedron oﬀers

adapters to attach such ﬁlters onto the meter.

1.1 QuickStart

1. Connect the SQM-LU meter to the computer with the supplied USB cable. Wait for any device drivers to automatically load (if required). You may have to visit www.FTDIchip.com to get the latest VCP drivers if they do not get installed automatically.

2. Ensure that your computer date and time is up-to-date.

3. Install and launch UDM (Unihedron Device Manager software supplied on the CD from your File Manager).

4. Click the “Find” button to ﬁnd attached devices, then click on the SQM-LU that you connected.

5. Click on “Reading” to get a reading from the SQM-LU.

6. Logging and plotting can be done from the “Log Continuous” button.

1.1.1 Other software

• If you are using Windows, you may want to use Knightware SQM-Reader from www.knightware.biz/sqm .

• The CD contains examples of software (Perl, Python, etc.) for various functions that connect to the meter.

1.1.2 FITS integration

Some programs (listed below) gather information from the Unihedron Sky Quality meter products and insert that data into the Flexible Image Transport System (FITS) header.

• MaxPilote (Freeware) incorporates SQM readings from an SQM-LE/SQM-LU into the FITS header while at the same time provide constant readings in a live and updated Data Window.

• CCDAutoPilot

• FITS4Win2 uses the MPSAS keyword for sorting and ﬁltering image ﬁles.

1.1 QuickStart

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2 Measurements

The SQM-LU provides readings in Magnitudes per square arcsecond, abbreviated as: mpsas, and written mathematically

mag

Mpsas is a logarithmic measurement which means that large changes in sky brightness correspond to relatively small numerical changes. A diﬀerence of 5 magnitudes is a factor of 100 times the intensity. Therefore a sky brightness 5.0 darker corresponds to a reduction in photon arrival rate of a factor of 100.

The following schematic gives a rough idea of how to interpret the readings of the SQM:

Magnitudes are an astronomical unit of measure for object brightness. Brighter objects have a lower magnitude and darker objects have a higher magnitude value. For example; a star that is 6th magnitude is brighter than a star that is 11th magnitude.

The star Vega is used a the reference point of ≈ 0 magnitude. Table 2.1 shows the apparent magnitude of some common known celestial objects.

arcsec

mag

arcsec

Figure 2.1: Mpsas interpretive scale

Table 2.1: Apparent Magnitudes of Known Celestial Objects adapted from [2]

App. Mag. Celestial Object

−26.73 Sun

−12.6 full Moon

−4.7 Maximum brightness of Venus

+0.03 Vega, the original zero point

+6 Faintest stars observable with naked eye

+27

+30

Faintest objects observable in visible light with 8m ground-based telescopes

Faintest objects observable in visible light with Hubble Space Telescope

Arcsecond is the deﬁnition of an arc being divided up into seconds as follows.

1. There are 360 degrees in a circle.

2. There are 60 arcminutes in a degree, and 21600 arcminutes in a circle.

3. There are 60 arcseconds in an arcminute, and 1296000 arcseconds in a circle.

Square arcsecond (arcsec2) is the area covered by a square measuring 1arcsec × 1arcsec .

2.1 Getting accurate readings

Magnitude per square arcsecond is the deﬁnition of brightness in magnitudes spread out over one square arcsecond of the sky. For example; if the SQM provides a reading of 20.00 mpsas, that would be like saying that a light of a 20 magnitude star brightness was spread over one square arcsecond of the sky.

The ”magnitudes per square arcsecond” numbers are commonly used in astronomy to measure sky brightness. More details can be found at www.stjarnhimlen.se/comp/radfaq.html

Each magnitude lower (numerically) means just over 2.5 times as much more light is coming from a given patch of sky. A change of 5 mags/sq arcsec means the sky is 100x brighter.

Also, a reading of greater than 22.0 is unlikely to be recorded and the darkest we’ve personally experienced with the SQM is 21.80.

2.1 Getting accurate readings

Various factors will cause the night sky brightness to ﬂuctuate. Taking more readings will be useful in ruling out spurious events. The SQM gathers light for at least a one second period, and the brightness report is based on the light that was accumulated during that time.

At the darkest sites, natural variations in conditions such as airglow and the brightness of the zodiacal light are limiting factors.

Prevent artiﬁcially high (dark) readings by ensuring that there is nothing blocking the view of the sensor. Avoid taking readings near trees or buildings that may block the sensor.

Prevent artiﬁcially low (bright) readings by ensuring that there are no lighted objects (street lamps, the moon, etc.) that shine into the sensor at any angle.

2.1.1 Seeing conditions

The apparent blurring/transparency and twinkling (scintillation) of stars is due to wind in the upper atmosphere that causes water molecules to distort the light from space.

Stars are too small in comparison to the entire SQM ﬁeld of view, so scintillation is not expected to alter the SQM reading signiﬁcantly.

2.1.2 Light pollution

Undesirable artiﬁcial light that reaches you is considered to be light pollution. Much of this light comes from outdoor illumination of parking lots, street lamps, oﬃce buildings, advertising signs, etc..

Other causes of extra light in the night sky are listed below:

Aurora

Charged particles emitted from the Sun are directed to the poles of the earth by the Earth’s magnetic ﬁeld. These particles collide with atoms in the atmosphere and cause light to be emitted. Aiming the meter at the polar regions during Aurora Borealis (in the North) or Aurora Australis (in the South) will reduce the reading (lighter). Aiming the meter towards the equator will increase the reading (darker) under these conditions.

Airglow

Airglow is light produced by various phenomenon in the atmosphere which prevent the sky from being totally dark. Eﬀects of the magnetic poles of the Earth may cause airglow to be brighter near the poles.

Unihedron SQM-LU Operator’s Manual - 20170728 11

2 Measurements

The Milky Way

As one goes to sites with darker surface brightnesses, the fraction of the total light received by the SQM-LU which can be attributed to the Milky Way bulge increases and so the “oﬀset” in mpas will be larger (due to the Milky Way.)

The northern view of the Milky Way contributes about 0.10 mpsas under 21.5 mpsas (moonless) skies.

The southern view of the Milky Way might be as big an eﬀect as 0.56 mpsas in dark skies where it goes near-overhead.

For more information, see Surface Photometries of the Milky Way (Schlosser+ 1997) vizier.u-strasbg.fr/ftp/cats/VII/199/ReadMe

Moisture

Clouds, fog, and mist will reﬂect artiﬁcial light back down to the Earth causing a brighter (lower) reading. If there is no artiﬁcial light, then clouds may prevent starlight from coming to you and the reading will be darker (higher). This extra-dark situation can occur in very isolated areas like mountain tops, the ocean, or the desert. You will have to be aware of this special situation when analyzing readings.

Volcanic eruptions

Dust released into the atmosphere by volcanoes can reﬂect light from the surface of the earth back down. In a dark location this dust will prevent the light from stars and Milky Way and produce a darker (higher) reading.

Zodiacal light

The sunlight reﬂected of oﬀ dust particles in the ecliptic plane of our solar system is called zodiacal light.

The amount of light will be diﬀerent depending on whether the meter is pointed to the poles or plane of the solar system. It is likely to have less than 2% eﬀect. The primary reason for this small eﬀect is that the brightest and widest part of the zodiacal light is nearest the horizon where the SQM has almost no sensitivity (due to it being a primarily zenith-looking device). The portions at higher altitude are the narrowest and faintest and they would barely creep into the sensitivity cone of the SQM.

2.1.3 Other luminance scales

Candela per square meter (cd/m2) is commonly used by lighting engineers.

To convert the SQM mpsas reading to cd/m2, use Equation (2.1):

[cd/m2] = 10.8 × 104× 10

Naked eye limiting magnitude (NELM)

Quite often astronomers will refer to a sky by the darkest star they can see, for example a “6th magnitude sky”, in that case you can see 6th magnitude stars and nothing dimmer like 7thmagnitude stars. The term “6thmagnitude skies” is very subjective to a persons ability to see in the night, for example an older person might say “5thmagnitude skies” but a young child with better night vision might say “7thmagnitude skies”.

Nobody has performed the task of deﬁning a relationship between the two methods of sky brightness ( x magnitude skies and magnitudes per square arcsecond) -- probably because one is subjective and the other is objective and a wide variety of people would have to be polled.

An approximation exists for the conversion between NELM and MPSAS. You can use an NELM converter[5] created by SQM user K. Fisher to do that conversion, or the chart shown in Figure 2.2 and Equations (2.2) and (2.3).

(−0.4×[mag/arcsec2])

(2.1)

12 Unihedron SQM-LU Operator’s Manual - 20170728

2.1 Getting accurate readings

Figure 2.2: Mpsas vs NELM

Convert NELM (V mags) to MPSAS (B) sky brightness [3]

= 21.58 − 5 × log(10

mpsas

(1.586−NELM/5)

− 1) (2.2)

Convert MPSAS (B) sky brightness to NELM (V mags) [4]

NELM = 7.93 − 5 × log(10

(4.316−(Bmpsas/5))

+ 1) (2.3)

NSU

A newly proposed term to deﬁne “Natural Sky Units”:

In “natural sky units” (radiance relative to an assumed natural radiance of 21.6 magSQM/arcsec2, see methods), the range was 0.22 - 2200 NSU. Before the introduction of anthropogenic light, the radiance of a patch of sky near zenith on moon-free nights is likely to have been nearly always within the range 21 (galactic center near zenith) to 24 mag/arcsec2 (very thick clouds), or 0.1 - 1.7 NSU.[1]

Unihedron SQM-LU Operator’s Manual - 20170728 13

3 Theory of operation

3.1 Light measurement

The SQM-LU measures the darkness of the night sky to provide readings of magnitudes per square arc second through a USB connection, and is capable of internally recording readings.

A light sensor (TSL237) provides the micro-controller with a light level, and readings from the temperature sensor are used to compensate the light sensor readings through the range of operating temperatures.

3.2 Communication to the PC

Commands sent from a PC through the USB cable to the USB interface are relayed to the micro-controller.

The micro-controller responds to commands by sending data strings to the USB interface which are then relayed to the PC.

Readings are gathered asynchronously by the micro-controller. Requests from the PC are buﬀered and dealt with as time permits.

4 Speciﬁcations

USB connection USB B connector.

5m USB A to USB B cable supplied. USB FTDI VCP driver, serial port emulator at 115200baud.

Physical Size 3.6” x 2.6” x 1.1”

Meter precision Each SQM-LU is factory-calibrated. The absolute precision of each meter is

believed to be ±10% (±0.10 mag/arcsec2). The diﬀerence in zero-point between each calibrated meter is typically ±10% (±0.10 mag/arcsec2)

Power requirement 18mA (from the 5V USB connection).

Operating temperature range -40◦C to 85◦C

Temperature Accuracy ± 2◦C maximum at 25◦C

Temperature update rate 4.3 seconds, 256 samples taken at 60Hz then averaged.

Figure 4.1: Front of unit

Figure 4.2: Back of unit

5 Hardware connections

The SQM-LU requires one connection to a USB hub or a PC for conﬁguring the device and recovering the readings as shown in Figure 5.1.

Figure 5.1: Wired connection

The maximum length cable per the USB speciﬁcation is 15ft (3m). USB extenders exist on the market, some work up to 198ft (60m).

6 Software development

The SQM-LU uses the FTDI FT232R chip to communicate as a standard serial port device at 115200 baud using the FTDI software drivers which are available for all major operating system platforms. Drivers are available from www.ftdichip.com .

Once the driver is installed, commands can be sent to the SQM-LU using a serial terminal emulator to the serial communications port that the device routes to.

When connecting the SQM-LU to a PC where the FTDI device driver is loaded, the serial port label will be determined at connection time.

Each SQM-LU has a unique serial number usually with a preﬁx of “FT........”. This serial number can be used to

identify the exact SQM-LU device from other USB devices.

6.1 Writing your own software interface

All of the commands and responses of the SQM-LU are documented in Section 8.

To communicate with the SQM-LU, the following general steps are required:

1. A serial 115200 baud connection must be made to the serial port assigned to the SQM-LU.

2. Data commands are sent to the SQM-LU, and it responds with a string of characters.

3. Close the serial port so that other programs can access the SQM-LU. Note: Only one connection can be made to the SQM-LU at a time. Therefore leaving a connection open constantly prevents other connections from being made.

Various examples of reading from the SQM devices are supplied on the CD and available at the Unihedron website. Below is an example using Perl to read the SQM USB device:

Listing 6.1: Read SQM-LU using Perl

#!/usr/bin/perl

#Filename: read-sqmlu.pl #Description: Utility to read Unihedron Sky Quality Meter-LU (USB model)

# Define the required module

use Device::SerialPort;

# Open and configure serial port

$port= Device::SerialPort->new("/dev/ttyUSB2"); $port->user_msg(ON); $port->baudrate(115200); $port->parity("none"); $port->stopbits(1); $port->databits(8); $port->handshake("none"); $port->write_settings || undef $port; $port->read_char_time(1); # Wait for each character

# Send request to SQM

$port->write("rx\r");

# Get response from SQM

($count,$saw)=$port->read(255);

# Close the port so that other programs can use the SQM

$port->close;

6 Software development

# Print the SQM result to the screen

printf("%s", $saw);

The above program prints a result like this:

r,-09.42m,0000005915Hz,0000000000c,0000000.000s, 027.0C

6.2 Pascal

The UDM program contains many examples of ﬁnding the SQM devices and reading data from them. It is open source and written in Lazarus/FreePascal. The source ﬁles for UDM are available here:

unihedron.com/projects/darksky/cd/udm/ .

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7 Unihedron Device Manager

The Unihedron Device Manager (UDM) program is intended for use in maintaining and testing the Unihedron connected Sky Quality Meter products. Windows, Mac, Linux versions of UDM area available on the supplied CD. It is used to:

• Read version information.

• Request readings.

• Read and set calibration data.

• Read and set all other meter parameters.

• Install new ﬁrmware.

• Setup and retrieve data from datalogging meters.

• Continuously log data from connected meters.

7.1 Getting UDM

UDM is supplied on the CD that shipped with the SQM-LU. The latest version of UDM is available at the Unihedron website at this location

www.unihedron.com/projects/darksky/cd/

7.2 Installation

7.2.1 System requirements

The UDM is a fairly simple (but large) program which should run suﬃciently on any present-day computer under the Windows, Mac, or Linux operating systems.

7.2.2 Windows

The Windows version of UDM is in a setup.exe style ﬁle located in the Windows subdirectory of the CD, for example:

\Windows\setup1.0.0.38.exe

Simply double-click on that ﬁle to start the installation procedure.

7.2.3 Mac

The Mac OSX version of UDM is a dmg ﬁle located in the Mac subdirectory of the CD, for example:

/Mac/udm.app.dmg

Drag the app to the /Applications directory.

7.2.4 Linux

The Linux version of UDM is available in a Debian package separately for both 32bit and 64bit systems located in the Linux directory of the CD, for example:

/Linux/udm 20140821-1 i386.deb

Open the ﬁle with package installer program like GDebi.

7 Unihedron Device Manager

7.3 Operation

After starting UDM, a list of found devices should appear, if your device is not listed on the screen, try clicking “Find” once more to search for connected devices.

If more than one SQM device is found, then you will have to select (click) on one of the devices, otherwise if only one

device is found, then click on “Version” or “Reading” of the information tab for more information.

The tabs can be used to select various functions when working with your selected device. These tabs and their functions

are described further in this document.

7.3.1 Start up

After starting the UDM program, a splash screen shown in Figure 7.1 is temporarily shown while the program searches for attached devices.

Figure 7.1: Splash screen

1. UDM searches for attached USB devices ﬁrst. This step is fairly quick (a few seconds).

2. UDM then searches for attached Ethernet devices within the reach of the Ethernet network but not outside a ﬁrewall. This step may take about 30 seconds.

If no devices are found, then the main UDM program will be shown with the “found devices box” empty. You can

attach an SQM device to your computer and press the “Find” button to search for the newly connected devices.

If you know that an Ethernet device is connected but it does not show up, then a network problem may be the cause.

Also check the power connection to the SQM-LE.

If you know that a USB device is connected but it does not show up, then there may be a device driver issue. Check the USB device listing for your operating system. These USB devices should appear as a COMM port. Also, check the troubleshooting notes in section 13 on page 62 for possible solutions.

7.3.2 Main screen

The main screen of UDM consist of the following sections:

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7.3.3 Main menu

7.3 Operation

1. Window controls

2. Menu

3. Found devices box

4. Selected device details

5. Information section

6. Status bar

The main menu of UDM consists of the items; File, View, Tools, Help as deﬁned below.

7.3.4 File menu

The ﬁle menu is used for: opening ﬁles, ﬁnding newly attached devices, and quitting the program as shown in Figure 7.2.

Figure 7.2: File menu

File : Open

The “File : Open” menu item is used to open up previously stored log ﬁles or calibration reports.

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7 Unihedron Device Manager

Figure 7.3: File Open dialog

File : Find USB

The “File : Find USB” function can be used to only ﬁnd attached USB devices and ignore possible Ethernet devices. The hotkey Ctrl+U can also be used instead of the mouse.

File : Find Ethernet

The “File : Find Ethernet” function can be used to only ﬁnd attached Ethernet devices and ignore possible USB devices. The hotkey Ctrl+E can also be used instead of the mouse.

File : Quit

The “File : Quit” menu item is used to close the UDM program.

The program can also be closed from the window panel “X”.

View menu

The view menu allows you to enable various tabs and check other settings of the UDM program.

Figure 7.4: View menu

View : Simulation

Click on “View : Simulation” to toggle visibility of the “Simulation” tab. The Simulation tab can be used to send requests to the SQM-LU to simulate conversions of frequency and period to light meter values. See page 36 for more details.

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7.3 Operation

View : Conﬁguration

Click on “View : Conﬁguration” to toggle visibility of the “Conﬁguration” tab. The Conﬁguration tab is used to conﬁgure the SQM with its calibration values when calibrated light and dark settings are being performed.

View : Log shows a window of commands and responses sent to and received from the SQM during this session of running UDM. Some excessively repetitive commands are suppressed from this listing.

Figure 7.5: View : Log

View : Directories shows the directory paths used by UDM to store and retrieve data.

Figure 7.6: View:Directories

Logs Directory Path shows the path where logged records are kept. These logged records are created when using the “Log one Record” or “Log Continuously” features. Also, log ﬁles from data-logging meters will be stored here from the “Retrieve All” function.

The “Logs Directory Path” path can be changed from its default by pressing the folder button the right. After the path has been changed, new log ﬁles will be stored in that new folder.

TZ database path The Time Zone information is required for datalogging purposes because the timestamp is logged as UTC. Since time zones change over the years, the entire Time Zone database is required and hence distributed with UDM and stored at the displayed “TZ database path”. This path is not changeable.

The Time Zone database is taken from: http://www.twinsun.com/tz/tz-link.htm

Firmware ﬁles path The ﬁrmware for the SQM-LU can be updated or reverted using UDM. These ﬁrmware ﬁles are stored at the displayed ﬁrmware ﬁles path. This path is not changeable.

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7 Unihedron Device Manager

Data Directory is the place where some data ﬁles are kept, speciﬁcally the change-log for UDM and ﬁrmware ﬁles. This path is not changeable.

Conﬁgﬁle path is the place where UDM stores its conﬁguration about the program and attached SQM devices. This path is not changeable.

View : DL Header shows the Data-logger header editing page. See the information at www.darksky.org/measurements for a detailed description of each ﬁeld.

Figure 7.7: Data logging header

DL : Position can be changed by pressing the Edit button which calls up the following dialog:

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Figure 7.8: Set Location dialog

7.3 Operation

The “Set location” dialog is used to type in your location and have it veriﬁed on the world map. Use the following steps to set the location:

1. Type the exact location coordinates (in degrees) of the SQM-LU into the “Desired” ﬁelds.

2. The mouse pointer can be used to select an approximate location if you are not sure of the exact coordinates.

3. The “Elevation” entry is optional as it is not used for anything yet.

4. Press the “Apply” button when you are satisﬁed with the desired values. Note: The “Apply” button will only be enabled if there is a diﬀerence between the desired and actual values.

5. Press “Close” when you are satisﬁed with the actual values.

The “Local timezone region” and “Local timezone name” are required by UDM to calculate local times of the recorded

data before storing to disk. UTC timestamps are stored in the SQM-LU.

The cover oﬀset is a text only ﬁeld that indicates what oﬀset was used on the calibration data of the SQM-LU.

7.3.5 Tools menu

Tools : old log to dat

The “old log to dat” tool is used to convert the original .log ﬁles that UDM created before the .dat ﬁle was made standard. Figure 7.9 shows the setup dialog for conversion.

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7 Unihedron Device Manager

Figure 7.9: Tool : old log to dat

Tools : dat to Moon csv

The “dat to Moon csv” tool is used to convert .dat ﬁles to a csv ﬁle that contains Moon data using algorithm library from Andreas H¨orstemeier [6].

The value for “Moon phase angle” reported in the .csv is:

• 180 or -180 = Full Moon

• 0 = New Moon

• Positive numbers Waxing (growing)

• Negative numbers Waning (shrinking)

Figure 7.10: Tool : dat to Moon csv

Press the “Select ...” button shown in Figure 7.10 to select the ﬁle and start the conversion process.

Tools : Comm terminal

The “Comm terminal” is a communication terminal window used for sending manual commands and viewing the response of the selected (from the found devices window) device.

26 Unihedron SQM-LU Operator’s Manual - 20170728

Figure 7.11: Tool : Comm terminal

Tools : DL retrieve

The “DL retrieve” tool is used for Vector model to pull in data ﬁles that were stored on disk previously.

7.3.6 Help menu

7.3 Operation

Figure 7.12: Help menu

Help : Cmdline Info shows the commands that can be used when starting UDM from the command line.

Help : Version Info shows the detailed version information for the UDM software.

Help : About displays a simple screen with the version identiﬁer.

Figure 7.13: Help : About

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7 Unihedron Device Manager

Found devices box shows all the connected SQMs available that UDM can ﬁnd from this computer.

If only one device is found, then UDM auto-selects it and gathers the version information for that selected device.

Figure 7.14: Found device (single)

If more than one device is found, then UDM does not select any of the devices. You may select the desired device by clicking in the found devices box on the SQM that you want to know more about. Once you select the device, then the connection details are displayed. Clicking on the “Version” or “Reading” button will gather more information from the meter.

Figure 7.15: Found device (multiple)

Device details shows the connection details of the selected SQM listed in the “Found devices” box.

The USB “Port” ﬁeld is editable so you may enter your own port that might not be deﬁned in the found box. See Figure 7.16.

Figure 7.16: USB connection details

The Ethernet IP and port ﬁelds are editable so you may enter your own IP and port that might not be deﬁned in the found box. The default port number for the SQM-LE is 10001. See Figure 7.17.

Figure 7.17: Ethernet connection details

The RS232 ﬁelds are editable so you may enter your own port and baud rate. The baud rate for the SQM-LR is 115200. See Figure 7.18.

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7.4 Information tab

Figure 7.18: RS232 connection details

7.4 Information tab

The information tab is used to show information about the version and the reading of the selected SQM.

Press the “Version” button for an updated list of data about the device version, and press the “Reading button” for an updated list of data about the device reading.

Figure 7.19: Information tab

The Header button calls up the data ﬁle header entry screen, see the datalogging Header section on page 24 for more information. This header information is used when storing logged data to the disk with the “Log one record” or “Log continuous” functions described below.

Log one record gathers one data record from the connected SQM and stores that information to a data log ﬁle on the disk in the “Logs directory path”. The location of the ﬁle can be identiﬁed and changed by “View : Directories”. The log ﬁle can be accessed later from the “File : Open” menu.

7.5 Log Continuous

The “Log continuous” function allows data from the connected SQM device to be logged repetitively as shown in Figure

7.20.

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7 Unihedron Device Manager

Figure 7.20: Log Continuously screen

Log Continuous Trigger options must be deﬁned before logging, see Figure 7.21 for possibilities:

Figure 7.21: Log Continuously Trigger tab

To operate the continuous logging function:

1. Select the frequency of logging from the trigger tab.

2. Press the “Record” button. The records are stored in a logﬁle whose location is shown in the “Logﬁle name” area. A new logﬁle is automatically created at the beginning of each day (at local time 0:00).

3. Press the “Stop” button when you want to stop the recording process.

4. Log ﬁles can be accessed by the “File : Open” menu selection or by pressing the “folder” button shown in the “Log Continuously” screen.

5. Press “Close” when done with the continuous logging feature.

Threshold setting A threshold for recording readings can be set before starting recording. Any reading greater or equal to this threshold value will be recorded in the log ﬁle.

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7.5 Log Continuous

Figure 7.22: Log Continuously Threshold

A threshold of 0 will allow all readings to be recorded. The threshold indicator will turn green if the threshold of the triggered reading is met (recording) and red if the

triggered reading is below the threshold (no recording).

The threshold value is saved in the registry conﬁguration ﬁle when it is changed. Changes can only be made while not

recording.

An override from the command line options (-LCTH,x) can be made. The override will only take eﬀect for the current

session and will not alter the saved conﬁguration.

Annotation settings While the “Log Continuous” mode is recording data, annotations can be made to the log ﬁle records with hotkeys. The Annotation tab allows the deﬁnition of hotkeys and their associated annotation text that will appear at the end of an annotated record.

Figure 7.23: Log Continuously Annotation tab

Persistent annotation The “Persistent” mode makes the annotated text persistently appear at the end of each logged record after the ﬁrst time the hotkey is pressed.

Without “Persistent” checked, annotation text is only appended to a record when the hotkey is pressed, and other

records have no annotation text.

Synchronized annotation The “Synchronized” mode postpones annotation requests until the next scheduled record so that the annotated text is synchronized with scheduled triggered recordings.

Without “Synchronized” checked, the hotkey will immediately trigger a record log, and the associated annotation text

will be appended to that triggered record.

GPS UDM will read the data produced from an externally connected USB or serial GPS receiver.

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7 Unihedron Device Manager

Figure 7.24: Log Continuously GPS tab

Enter the port name into the Port ﬁeld, then enable the GPS. Once enabled, UDM scans the GPS port for three NMEA

words.

Upon succesful parsing of the GPS data, UDM illuminates (with bright green) the associated indicators (GPRMC,

GPGGA, GPGSV). If too much time passes, the indicators fade to black.

The signal strength group shows the signal to noise ratio (SNR) for all visible satellites. The satellite number is displayed

below each signal strength meter.

The location, speed, time, and status information is displayed as it is received. If the GPS is enabled before logging, then the logﬁle is forced to ”MOVING” platform mode, and ﬁve ﬁelds (latitude,

longitude, elevation, speed, number of satellites in view) are appended to each record.

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7.6 Calibration tab

The Calibration tab is used to show and set the calibration data for the selected SQM device.

Figure 7.25: Calibration tab (initial)

7.6 Calibration tab

Press the “Get Calibration Info” button so that the updated calibration data is brought in from the SQM on to the

Actual values boxes as show below.

Figure 7.26: Calibration tab (populated)

Use the following steps to change the calibration values:

1. Enter the new calibration data on the left side entry box (Desired values column).

2. Press the associated “Set” button.

3. The value is sent to the SQM, and then conﬁrmed in the right side box (Actual values column).

Note that temperatures set in to the SQM use their own resolution and may not be reﬂected as the same value entered. For example. 24.7◦C might read back as 24.8◦C.

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7 Unihedron Device Manager

The original factory calibration values were provided on a paper with the shipped unit. If you have lost this information,

please contact Unihedron to have the information emailed.

7.7 Report Interval tab

The Report Interval tab is used to show and set the report interval information for the selected SQM. Report interval settings are used to control the SQM to send readings out at a regular rate (in seconds) and only if darker than a speciﬁed threshold value. See section 8.6 on page 53 for more information about “Interval reporting”.

Figure 7.27: Report interval tab

Use the “R” button to temporarily set the value in to RAM for experimentation. The new value will be used instantly.

The RAM value is set to the EEPROM value on power-up.

Use the “E/R” button to set the value in to EEPROM and RAM. The new value will be used instantly and also after

power up.

Report interval is measured in seconds (i.e. 300 = 5 minutes). Report threshold is measured in Magnitudes per square arcsecond (mpsas), a larger positive value is darker.

7.8 Firmware tab

In a case where new ﬁrmware is supplied by Unihedron to correct bugs or add features, use this tab to select and load ﬁrmware in to the SQM-LU.

All available versions of ﬁrmware are shipped with the UDM software package in case you want to revert to an earlier

ﬁrmware version for testing purposes. New ﬁrmware versions are announced on the Unihedron forum.

Figure 7.28: Firmware tab

34 Unihedron SQM-LU Operator’s Manual - 20170728

7.9 Conﬁguration tab

Follow these steps to load new ﬁrmware:

1. Press the “Select Firmware” button to choose the ﬁrmware ﬁle to load in to the SQM as shown in Figure 7.29:

Figure 7.29: Firmware selection

2. Select the desired ﬁrmware ﬁle then press “Open”.

3. The “Load ﬁrmware” button will be enabled and you can press it now to start loading the ﬁrmware in to the SQM-LU. The status bar will indicate successful completion when the ﬁrmware has been completely loaded.

7.9 Conﬁguration tab

The “Conﬁguration tab” shows the factory-set calibration values.

Calibration is performed at the Unihedron factory. A new calibration using a calibrated light source and darkroom can be performed by following the instructions on the right side of the screen. The calibration report can be logged to a data ﬁle and also printed out from this screen.

Figure 7.30: Conﬁguration tab

Warning conﬁrmations as shown in Figure 7.31 and Figure 7.32 are shown when trying to calibrate the unit yourself:

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7 Unihedron Device Manager

Figure 7.31: Light calibration conﬁrmation

Figure 7.32: Dark calibration conﬁrmation

7.9.1 Sensor arrangement

For documentation purposes, the SQM-LU can store information on the sensor arrangement (starting at ﬁrmware feature 35 and above). The type of Lensholder, Lens, and Filter can be deﬁned.

Figure 7.33: Sensor arrangement

7.10 Simulation tab

The “Simulation” tab is enabled from the View menu.

The “Simulation” tab allows the simulation of raw light sensor values for experimentation purposes. The “Start” button initiates feeding the range of values to the internal formulas of the SQM-LU and results are displayed on this tab. Raw temperature conversions are detail in Eq: 8.1 and 8.2. The simulation will stop once all the steps are complete or when the “Stop” button is pressed.

Figure 7.34: Fig:Simulation tab

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7.10 Simulation tab

When using the Simulation mode of the SQM-LU, make sure that nothing else interrupts the sequence of readings such as external programs reading from the SQM-LU, or settings of Interval reporting inside the SQM-LU.

7.10.1 Simulation from ﬁle

The “From ﬁle” button sends csv data from simin.csv (in the log ﬁle directory) to the SQM-LU in simulation mode and puts the output into simout.csv. The format of the csv is shown in Table 7.2:

Table 7.2: simin.csv ﬁeld description

Position Example value Description

1 3000 Period in counts.

2 30 Frequency in Hz.

3 20.3 Temperature in◦C.

Listing 7.1: simin.csv example

0,568380,24.8 72970,6,13.2

The resultant output records will be shown on the screen and saved in simout.csv (in the log ﬁle directory) in the form of simulated result shown in section 8.7 as in the example shown in Listing 7.2:

Listing 7.2: simout.csv example

# Simulation from file. # UDM version: 1.0.0.43 # Unit information cx: i,00000004,00000003,00000032,00000704 # Calibration cx: c,00000019.80m,0000107.511s, 028.3C,00000008.71m, 029.3C S,0000000000c,0000568380f,0000000232t,r, 00.00m,0000568380Hz,0000000000c,0000000.000s, 024.8C S,0000072970c,0000000006f,0000000196t,r, 17.79m,0000000006Hz,0000072970c,0000000.158s, 013.2C

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7 Unihedron Device Manager

7.11 Accessory options

Some meters can be equipped/retro-ﬁtted with optional accessories if they include ﬁrmware feature version ≥40.

See section 8.4 for details on the accessory commands.

The accessories tab (shown in 7.35) is available when selecting a device that has the appropriate ﬁrmware:

Figure 7.35: Accessories tab

7.11.1 Humidity accessory

There are currently two types of I2C humidity sensors that have been tested; HIH8120, and HYT939. The selection can be made with the drop down combo-box on this tab.

Enabling this sensor allows the SQM-LU to poll the sensor once per second to gather a reading which can be requested later with the A1x command.

The refresh button requests the most recent value that the SQM-LU has collected.

The Status ﬁeld shows the status of the humidity sensor which is updated after the refresh button is pressed. The status is ‘N/C’ when the sensor is not connected.

7.11.2 Display accessory

A 4-digit 7-segment I2C display can be attached to the SQM-LU. Currently only the Sparkfun COM-11441 has ben tested.

This display shows the brightness reading in mpsas.

The brightness of the display can be ﬁxed at a level between 0-7 (dimmest to brightest), or can be automatically dimmed in bright conditions (depending on the mpsas reading).

The display can be either updated periodically (1Hz) or whenever a reading request is made.

7.11.3 LED accessory

The LED indicator accessory is mainly used for troubleshooting to identify either when readings are created or requested. The The LED blinks for 1/60th of a second.

The LED can blink either when the SQM-LU creates a reading, of when a reading is requested (using the rx command).

7.11.4 Relay accessory

The Relay accessory is mainly used for dew heater control. A 3.3V activated solid state relay can be connected directly to pin 23 of the microcontroller (25mA drive maximum).

When in Manual mode, the relay can be turned on or oﬀ.

When in Automatic mode, the relay is turned on when the mpsas reading is above the threshold and oﬀ when the mpsas reading is below the threshold.

Pressing the On/Oﬀ buttons while the realy is in automatic mode will switch it to manual mode.

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7.12 Command line parameters

UDM can be started from the command line. Other stored parameters (like timezone) will be recalled automatically. Here is the summary of options:

Table 7.3: Log continuous command line parameters

Parameter Description

-LCMS,x Every x seconds

-LCMM,x Every x minutes

-LCM,1 Every 1 minute on the minute

-LCM,5 Every 5 minutes on the 1/12th hour

-LCM,10 Every 10 minutes on the 1/6th hour

-LCM,15 Every 15 minutes on the 1/4 hour

-LCM,30 Every 30 minutes on the 1/2 hour

-LCM,60 Every hour on the hour

-LCR Start recording right away

-LCTH,x Threshold setting. Readings equal to or greater than x (in mpsas) get recorded. If x=0 then all readings are get recorded.

-LCMIN Minimize Application after Log continuous window starts up

Table 7.4: Select device command line parameters

Parameter Description

-SEI,x Select Ethernet device where x = IP address

-SEM,x Select Ethernet device where x = MAC address

-SUC,x Select USB device where x = communication portname i.e. /tty/USB0

-SUI,x Select USB device where x = ID number ex FTD12345

Table 7.5: Select device command line parameters

Parameter Description

-N Do not search for devices at startup. This cuts down startup time, the user must press the Find button to ﬁnd devices.

-P Display plotter window.

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8 Commands and responses

The SQM-LU accepts a sequence of characters as a command, then executes those commands and usually provides a response of a sequence of characters. The following details are useful when programming your own interface to send data to and receive data from the SQM-LU.

8.1 Commands

Commands consist of a string of characters. The ﬁrst character is the command type. The following is a list of the “Standard” commands:

Table 8.1: Summary of standard commands

Command Description

rx Reading request.

cx Calibration information request.

ix Unit information request (note lower case “i”).

zcalAx Arm Light Calibration command.

zcalBx Arm Dark Calibration command.

zcalDx Disarm Calibration command.

zcal5 Manually Set Light Calibration Oﬀset.

zcal6 Manually Set Light Calibration Temperature.

zcal7 Manually Set Dark Calibration Time Period.

zcal8 Manually Set Dark Calibration Temperature.

0x19 Reset micro-controller. Hexadecimal value 19. See the “Firmware Upgrade” chapter

on page 60 for more details.

: Intel Hex ﬁrmware upgrade initiation. See the “Firmware Upgrade” chapter on

page 60 for more details.

P...x Set period (in seconds) for interval reporting to EEPROM and RAM for booting

and immediate use. Firmware feature=13.

p...x Set period (in seconds) for interval reporting to RAM for immediate use. Firmware

feature=13.

T...x Set threshold (in

booting and immediate use. Firmware feature≥13.

t...x Set threshold (in

Firmware feature≥13.

Ix Request interval settings (note upper case “I”). Firmware feature≥13.

sx Request reading of internal variables.

S...x Simulate internal calculations.

mag

arcsec

mag

arcsec

) for interval reporting only to EEPROM and RAM for

) for interval reporting only to RAM for immediate use.

8.2 Response details

8.2.1 Reading request

The “Reading” request “rx” or “Rx” commands the SQM-LU to provide the current darkness value as well as all variables used to generate that result.

Readings produced by this request are averaged internally by using the last 8 readings and shifting those values through an 8 cell buﬀer then summing and dividing by 8. Use the “ux” command to get the un-averaged and most recent value. Averaging is only performed on period-mode readings (when the light sensor frequency is below 128Hz). Frequency mode readings (above 128Hz) are automatically averaged because the reading is taken from a one second sampling of pulses.

The format of the response is shown in table 8.2:

Table 8.2: Reading request response

Column Example value Description

0 r Indicates that a reading is being returned.

2-8 06.70m Reading in

Leading space for positive value. Leading negative sign (-) for negative value. A reading of 0.00m means that the light at the sensor has reached the upper brightness limit of the unit.

10-21 0000022921Hz Frequency of sensor in Hz.

23-33 0000000020c Period of sensor in counts, counts occur at a rate of 460.8 kHz

(14.7456MHz/32).

35-46 0000000.000s Period of sensor in seconds with millisecond resolution.

48-54 039.4C Temperature measured at light sensor in degrees C.

Leading space for positive value. Leading negative sign (-) for negative value.

55-56 Carriage return (0x0d), Line feed (0x0a).

mag

arcsec

An example of the response is:

r, 06.70m,0000022921Hz,0000000020c,0000000.000s, 039.4C

0123456789 123456789 123456789 123456789 123456789 123456

Future versions of this reading string will only modify reported values beyond position 54. Characters 0 to 54 may be considered stable.

A special case “Rx” command returns the serial number in the same format as the interval report does. See page 53 “Setting Interval reporting parameters” for report details.

8.2.2 Unaveraged reading request

The “unaveraged reading” request “ux” commands the meter to provide the current darkness value as well as all variables used to generate that result. This readings is not averaged out like the “rx” command.

The format of the response is shown in table 8.3:

Table 8.3: Unaveraged reading request response

Column Example value Description

0 u Indicates that a reading is being returned.

Table continued on next page ...

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8 Commands and responses

Table 8.3 – continued from previous page

Column Example value Description

2-8 06.70m Reading in

mag

arcsec

Leading space for positive value. Leading negative sign (-) for negative value. A reading of 0.00m means that the light at the sensor has reached the upper brightness limit of the unit.

10-21 0000022921Hz Frequency of sensor in Hz.

23-33 0000000020c Period of sensor in counts, counts occur at a rate of 460.8 kHz

(14.7456MHz/32).

35-46 0000000.000s Period of sensor in seconds with millisecond resolution.

48-54 039.4C Temperature measured at light sensor in degrees C.

Leading space for positive value. Leading negative sign (-) for negative value.

55-56 Carriage return (0x0d), Line feed (0x0a).

An example of the response is:

u, 06.70m,0000022921Hz,0000000020c,0000000.000s, 039.4C

0123456789 123456789 123456789 123456789 123456789 123456

Future versions of this reading string will only modify reported values beyond position 54. Characters 0 to 54 may be considered stable.

8.2.3 Unit information

Unit information command “ix” provides details about the software in the micro-controller.

The format of the response is:

Table 8.4: Unit information request response

Column Example value Description

0 i Indicates that the unit information response is being returned.

2-9 00000002 Protocol number (8 digits). This will always be the ﬁrst 8 char-

acters (after the “i,” response). This value indicates the revision number of the data protocol to/from the SQM-LU. The protocol version is independent of the feature version.

11-18 00000003 Model number (8 digits). The model value identiﬁes the speciﬁc

hardware model that the ﬁrmware is tailored for.

20-27 00000001 Feature number (8 digits). The feature value identiﬁes software

features. This number is independent of the data protocol.

29-36 00000413 Serial number (8 digits). Each unit has its own unique serial num-

ber.

37-38 Carriage return (0x0d), Line feed (0x0a).

An example of the response is:

i,00000002,00000003,00000001,00000413

0123456789 123456789 123456789 12345678

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8.3 Calibration commands

8.3.1 Calibration information request

The calibration information request “cx” returns all data about the speciﬁc light sensor in the unit required to calculate a reading.

The format of the response is shown in table 8.5:

Table 8.5: Calibration information request response

Column Example value Description

0 c Indicates that the calibration information is being returned.

2-13 00000017.60m Light calibration oﬀset in

15-26 0000000.000s Dark calibration time period in seconds with millisecond resolution.

28-34 039.4C Temperature in degrees C measured during light calibration.

Leading space for positive value. Leading negative sign (-) for negative value.

36-47 00000008.71m Oﬀset of light sensor in

49-55 039.4C Temperature in degrees C measured during dark calibration.

Leading space for positive value. Leading negative sign (-) for negative value.

56-57 Carriage return (0x0d), Line feed (0x0a).

mag

arcsec

mag

arcsec

based on manufacturing reference.

An example of the response is:

c,00000017.60m,0000000.000s, 039.4C,00000008.71m, 039.4C

0123456789 123456789 123456789 123456789 123456789 1234567

8.3.2 Light calibration command

Calibration of the SQM-LU is done at the factory in a controlled light and temperature environment.

Executing the Light calibration command “zcalAx” arms the light calibration mode.

A calibrated light source of approximately 13.5fc is supplied to the sensor.

The format of the response is shown in table 8.6:

Table 8.6: Light calibration response

Column Example value Description

0 z Indicates that a “Calibration” response is being returned.

1 A Indicates Light Calibration mode.

2 a Indicates that the calibration is armed.

3 L L = Locked; Wait for unlock before calibrating after Arm command,

ﬁrmware upgrades are disabled. U = Unlocked; Calibrate immediately after Arm command, Enable ﬁrmware upgrade.

4-5 Carriage return (0x0d), Line feed (0x0a).

An example of the response is:

zAaL

012345

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8 Commands and responses

8.3.3 Dark calibration command

Dark Calibration is done at the factory along with Light calibration and calibration temperature recording.

Executing the dark calibration command “zcalBx” arms the dark calibration mode.

Dark calibration is performed in a completely dark environment. Check a reading to ensure that the period is correct after entering the dark environment, it could take a few minutes to collect an accurate dark period. A dark period of only a few seconds is too small.

The format of the response is shown in table 8.7:

Table 8.7: Dark calibration response

Column Example value Description

0 z Calibration response is being returned.

1 B Dark Calibration.

2 a Armed.

3 L L = Locked; Wait for unlock before calibrating after Arm command,

ﬁrmware upgrades are disabled. U = Unlocked; Calibrate immediately after Arm command, Enable ﬁrmware upgrade.

4-5 Carriage return (0x0d), Line feed (0x0a).

An example of the response is:

zBaL

012345

8.3.4 Disarm calibration command

The Disarm calibration command “zcalDx” disarms calibration modes from being triggered by the unlock mode.

The format of the response is shown in table 8.8:

Table 8.8: Disarm calibration response

Column Example value Description

0 z Calibration response is being returned.

1 x Indicates “All” calibration modes.

2 d Disarmed.

3 L L = Locked; Wait for unlock before calibrating after Arm command,

ﬁrmware upgrades are disabled. U = Unlocked; Calibrate immediately after Arm command, Enable ﬁrmware upgrade.

4-5 Carriage return (0x0d), Line feed (0x0a).

An example of the response is:

zxdL

012345

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8.3 Calibration commands

8.3.5 Manually set light calibration oﬀset

Calibration is done at the factory, however, in the case where calibration values must be restored or set to something else, this command allows a new calibration value to be placed into the meter.

Executing the command “zcal5########.##x” manually sets the light calibration oﬀset to the value speciﬁed in “########.##”. The units are

The format of the response is shown in table: 8.9:

Column Example value Description

0 z Calibration response is being returned.

2 5 Manual Set Light Calibration Oﬀset

4-15 00000017.60m Value that was set into EEPROM

16-17 Carriage return (0x0d), Line feed (0x0a).

An example of the response is:

z,5,00000017.60m

0123456789 1234567

magnitudes

arcsecond

Table 8.9: Response for manual setting of light calibration oﬀset

8.3.6 Manually set light calibration temperature

Calibration is done at the factory, however, in the case where calibration values must be restored or set to something else, this command allows a new calibration value to be placed into the meter.

The “Light calibration temperature” is the temperature of the meter when the meter was calibrated for its “Light calibration oﬀset”.

Executing the command “zcal6########.##x” manually sets the light calibration temperature to the value speciﬁed in “########.##”. The units areoC.

Note: The meter records the temperature in a raw value with diﬀerent resolution, so the reply back may not be exactly the same as the value sent.

The format of the response is shown in table: 8.10:

Table 8.10: Response for manually setting of light calibration temperature

Column Example value Description

0 z Calibration response is being returned.

2 6 Manual Set Light Calibration Oﬀset

4-9 019.0C Value that was set into EEPROM

10-11 Carriage return (0x0d), Line feed (0x0a).

An example of the response is:

z,6,019.0C

0123456789 1

8.3.7 Manually set dark calibration time period

Calibration is done at the factory, however, in the case where calibration values must be restored or set to something else, this command allows a new calibration value to be placed into the meter.

The “Dark calibration time period” is the amount of time that has elapsed for the light sensor to make one cycle while in complete darkness. The meter sets a time limit of 300 seconds on this value.

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8 Commands and responses

Executing the command “zcal7#######.###x” manually sets the light calibration oﬀset to the value speciﬁed in “#######.###”. The units are in seconds.

The format of the response is shown in table: 8.11:

Table 8.11: Response of manually setting dark calibration time period

Column Example value Description

0 z Calibration response is being returned.

2 7 Manual Set Dark Calibration time period.

4-15 0000300.000s Value that was set into EEPROM

16-17 Carriage return (0x0d), Line feed (0x0a).

An example of the response is:

z,7,00000300.00s

0123456789 1234567

8.3.8 Manually set dark calibration temperature

Calibration is done at the factory, however, in the case where calibration values must be restored or set to something else, this command allows a new calibration value to be placed into the meter.

The “Dark calibration temperature” is the temperature of the meter when the meter was calibrated for its “Dark calibration time period”.

Executing the command “zcal8########.##x” manually sets the light calibration oﬀset to the value speciﬁed in “########.##”. The units areoC.

Note: The meter records the temperature in a raw value with diﬀerent resolution, so the reply back may not be exactly the same as the value sent.

The format of the response is shown in table: 8.12:

Table 8.12: Response for manually setting of dark calibration temperature

Column Example value Description

0 z Calibration response is being returned.

2 8 Manual Set Dark Calibration temperature.

4-9 019.0C Value that was set into EEPROM

10-11 Carriage return (0x0d), Line feed (0x0a).

An example of the response is:

z,8,019.0C

0123456789 1

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8.4 Accessories commands

Some I2C accessory devices can be connected to the SQM-LU when using ﬁrmware feature version 44 and above. These devices are connected by way of retroﬁtted wiring inside the unit or a future back panel connector.

All of the SQM-LU accessory commands begin with “A” (upper case).

8.4.1 Humidity / Temperture sensor

Two I2C humidity/temperature sensors models can be connected to the SQM-LU. All commands (seen in table 8.13) to this accessory result in a response (seen in table 8.14).

Table 8.13: Humidity/temperature command summary

Command Description

A1Ex Enable the humidity temperature accessory.

A1Dx Disable the humidity temperature accessory.

Set the model number (where m =0-7) of the the humidity temperature accessory:

A1Mm x

A1x Report on the humidity temperature status.

0=HIH8120 1=HYT939 (Sold by ControlEverything and others)

Table 8.14: Humidity/temperature response summary

Position Example value Description

0 A,1, Conﬁrmation of humidity/temperature accessory command.

1 1, Accessory 1 (Humidity/temperature sensor).

2 e, E for enabled.

D for disabled.

3 m, Model number (where m =0-7):

0=HIH8120 1=HYT939 (Sold by ControlEverything and others)

4 s Status (0-3).

0 = Normal Operation, Valid Data that has not been fetched since the last measurement cycle. 1 = Stale Data: Data that has already been fetched since the last measurement cycle, or data fetched before the ﬁrst measurement has been completed. 2 = Sensor in Command Mode. 3 = Not used.

5 nnnnn Humidity(%RH) =

6 nnnnn Temperature(◦C) =

nnnnn

× 100%. 16383 when no connection.

214−2

nnnnn

× 165 − 40. 16383 when no connection.

214−2

Carriage return (0x0d), Line feed (0x0a).

An example response to “A1x” is:

A,1,E,1,0,07788,06202

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8 Commands and responses

8.4.2 Display accessory

An I2C 4-digit 7-segment display made by Sparkfun (model COM-11441) can be connected. All commands (seen in table

8.15) to this accessory result in a response (seen in table 8.16).

Readings that are too bright for the SQM-LU will show up as u u u u . Readings that are too dark for the meter will show up as t t t t .

Table 8.15: Display accessory command summary

Command Description

A2Ex Enable the display accessory.

A2Dx Disable the display accessory.

A2Fx Fixed mode of brightness.

Auto mode of brightness. Lowers brightness on dark nights.

A2Ax

A2Mn x Set the model of display (where n = 0-3).

A2Vn x Set the ﬁxed mode brightness (where n = 0-7).

Display at lowest brightness (30%) when greater than 19.00mpsas. Display at medium brightness (50%) between 17.00 to 19.00mpsas. Display at full brightness (100%) when less than 17.00mpsas.

A2Px Set the updating mode to periodically updating at 1Hz.

A2Rx Set the updating modeto updating when reading request is made.

A2x Report on the display status.

Table 8.16: Display accessory response summary

Position Example value Description

0 A, Conﬁrmation of display accessory command.

1 2, Accessory 2 (Display).

2 e, E for enabled.

D for disabled.

3 m, Model number (where m = 0-3).

4 m, F=Fixed mode.

A=Auto mode. See table 8.15 for description.

5 n, Fixed brightness level (where n = 0-7).

6 m P = periodically updating at 1Hz

R = updating when reading request is made.

Carriage return (0x0d), Line feed (0x0a).

An example response to “A2x” is:

A,2,E,0,F,2,R

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8.4 Accessories commands

8.4.3 LED accessory

For purposes of troubleshooting, an LED with series resistor can be connected to an internal pin of the SQM-LU. All commands (seen in table 8.17) to this accessory result in a response (seen in table 8.18).

Using the LED to indicate when a reading is being requested is an ideal method to determine if the controlling software is actually accessing the SQM-LU.

Table 8.17: LED accessory command summary

Command Description

A3Ex Enable the LED accessory.

A3Dx Disable the LED accessory.

Mode=Blink at reading creation.

A30x

A31x Mode=Blink at reading request.

A3x LED accessory status.

In bright sky conditions, readings are created once per second in frequency-mode. In darker sky conditions, the meter goes into perdiod-mode starting at 679Hz and lower, and LED will blink at a variable rate.

Table 8.18: LED accessory response summary

Position Example value Description

0 A, Conﬁrmation of display accessory command.

1 3, Accessory 3 (LED).

2 e, E for enabled.

D for disabled.

3 m, Model number (where m = 0-7).

0 = LED connceted to pin-13 through 1k resistor to ground.

4 m, Mode of operation (where m = 0-1):

0 = Blink at reading creation. 1 = Blink at reading request.

Carriage return (0x0d), Line feed (0x0a).

An example response to “A2x” is:

A,3,E,0,1

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8 Commands and responses

8.4.4 Relay accessory

A Solid State Relay (SSR) accessory may be connected to the SQM-LU for generic use or for purposes of implementing a dew-heater control. All commands (seen in table 8.19) to this accessory result in a response (seen in table 8.20).

Table 8.19: Relay accessory command summary

Command Description

A4x Get status of the relay accessory.

A40x Deactivate the relay accessory. Also places the accessory into manual mode.

A41x Activate the relay accessory. Also places the accessory into manual mode.

Set the mode of operation: 0=Light threshold activated.

A4Mn x

A4Tnn x

1=Dewpoint activation. 2=Heat activated. 3-6=future use. 7=Manual mode where only the A40x and A41x commands aﬀect the relay activation.

Set the darkness threshold for relay activation. Where nn is the the darkness threshold. The relay will be activated above this threshold. Monitoring is perfomed once per second.

Table 8.20: Relay accessory response summary

Position Example value Description

0 A, Conﬁrmation of display accessory command.

1 4, Accessory 3 (relay).

2 s, Status of device:

0 for deactivated relay. 1 for activated relay.

3 m, Mode of operation (where m =0-7):

0 = Light mode. 1 = Dewpoint mode. 2 = Heat mode. 7 = Manual mode.

4 nn Threshold of darkness (in mpsas) for automatic mode of operation.

5 ttt Temperature (◦C) used for dewpoint calculation.

6 hhh Humidity (%RH) used for dewpoint calculation.

7 ddd Dewpoint temperature (◦C) used for dewpoint calculation.

Carriage return (0x0d), Line feed (0x0a).

An example response to “A2x” is:

A,4,1,2,15,10,50,40,0

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8.5 Continuous reporting commands

The Continuous reporting features are somewhat experimental. A description of each feature follows:

Table 8.21: Summary of standard commands

Option Description

Reporting enabled Send a reading result every time it is available from internal computations. In

bright settings, a reading will be made available once per second, around 14mpsas, a reading will be available depending on the sensor response which is between 60+ times per second and 60 seconds in very dark settings.

Ideal crossover ﬁrmware Changes the crossover of reporting from original (around 15mpsas to 12.32mpsas

which results in better resolution across the entire range of possible readings.

Reporting compressed Send the above enabled reading out in a compressed format without extra text.

Report un-averaged Sends the above reading out from the un-averaged accumulator. Normally the

averaged reading is sent.

Table 8.22: Continuous reporting command summary

Command Description

Yx Get status of the continuous reporting features.

YRx Enable continuous reporting.

Yrx Disable continuous reporting.

YCx Enable new crossover ﬁrmware code.

Ycx Disable new crossover ﬁrmware code.

YPx Enable continuous reporting compression.

Ypx Disable continuous reporting compression.

YUx Enable un-averaged continuous reporting.

Yux Disable un-averaged continuous reporting.

Table 8.23: Response of all continuous reporting requests

Column Example value Description

0 Y Conﬁrmation of command.

1 r R = Continuous reporting enabled.

r = Continuous reporting disabled.

2 C C = Ideal crossover ﬁrmware code enabled.

c = Ideal crossover ﬁrmware code disabled.

3 p P = Continuous reporting compression enabled.

p = Continuous reporting compression disabled.

Table continued on next page ...

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8 Commands and responses

Column Example value Description

4 u U = Continuous reporting un-averaged readings enabled.

5-6 Carriage return (0x0d), Line feed (0x0a).

An example response is:

YrCpu

01234

Table 8.23 – continued from previous page

u = Continuous reporting un-averaged readings disabled.

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8.6 Setting Interval reporting parameters

For ﬁrmware feature ≥13, the SQM-LU is capable of sending timed interval reports. Each interval report is the same as the reading request report except that the serial number (feature ≥14) is attached at the end so that numerous reporting SQM-LUs can be distinguished from each other.

The format of the interval report is shown in table 8.24:

Table 8.24: Interval report

Column Example value Description

0 r Indicates that a reading is being returned.

2-8 06.70m Reading in magnitudes per square arc second.

Leading space for positive value. Leading negative sign (-) for negative value. A reading of 0.00m means that the light at the sensor has reached the upper brightness limit of the unit.

10-21 0000022921Hz Frequency of sensor in Hz.

23-33 0000000020c Period of sensor in counts, counts occur at a rate of 460.8 kHz

(14.7456MHz/32).

35-46 0000000.000s Period of sensor in seconds with millisecond resolution.

48-54 039.4C Temperature measured at light sensor in degrees C.

Leading space for positive value. Leading negative sign (-) for negative value.

55-63 00000413 Serial number (8 digits). Each unit has its own unique serial num-

ber.

64-65 Carriage return (0x0d), Line feed (0x0a).

An example is:

r, 06.70m,0000022921Hz,0000000020c,0000000.000s, 039.4C,00000413

0123456789 123456789 123456789 123456789 123456789 123456789 12345

8.6.1 Interval reporting period setting

Executing the command “P##########x” (note upper case “P”) sets the period of the timed interval reports to the EEPROM and RAM for booting and immediate use.

Executing the command “p##########x” (note lower case “p”) sets the period of the timed interval reports to RAM only for immediate use.

The units are seconds. For example, the command “p0000000360x” sets the reporting time to once every 360 seconds.

8.6.2 Threshold setting for interval reporting

Executing the command “T########.##x” (note upper case “T”) sets the threshold of the timed interval reports to EEPROM and RAM for boot and immediate use.

Executing the command “t########.##x” (note lower case “t”) sets the threshold of the timed interval reports to RAM for immediate use only.

The units are

magnitudes

arcsecond

. For example, t00000016.00x limits reporting to values only over 16.00

magnitudes

arcsecond

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8 Commands and responses

8.6.3 Interval setting response

Either making the request “Ix” (note upper case “I”) or any request to set the interval report setting produces the following response shown in table 8.25:

Table 8.25: Response of viewing or setting interval reporting parameters

Column Example value Description

0 I Interval settings from EEPROM and RAM are being returned.

2-12 0000000360s Interval period that was set into EEPROM.

14-24 0000300360s Interval period that was set into RAM.

26-37 00000017.60m Threshold value that was set into EEPROM.

39-50 00000017.60m Threshold value that was set into RAM.

51-52 Carriage return (0x0d), Line feed (0x0a).

An example response is:

I,0000000360s,0000000360s,00000017.60m,00000017.60m

0123456789 123456789 123456789 123456789 123456789 12

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8.7 Simulation commands

The following simulation commands help to determine the results of

mag

arcsec

readings derived from the light and temperature

sensors.

To read the internal simulation values, issue the “sx” command, the response is shown in table 8.26:

Table 8.26: Response of request for internal simulation values

Column Example value Description

0 s Conﬁrmation of the command.

1 , Separation character.

2-12 0000000360c Number of counts.

13 , Separation character.

14-24 0000000360f Frequency in Hz.

25 , Separation character.

26-37 0000000244t Temperature ADC value as seen by the CPU. See Equation 8.1 .

38-39 Carriage return (0x0d), Line feed (0x0a).

An example response is:

s,0000000360c,0000000360f,0000000360t

0123456789 123456789 123456789 12345678

To convert raw temperature value to degrees C:

raw×3.3

DegC =

1024

− 0.5

0.01

To convert degrees C value to raw temperature:

raw =

(DegC × 0.01 + 0.5) × 1024

3.3

To set the internal simulation values and read the calculated response, issue the “S...x” command as detailed in Table

8.27. The result of that command is shown in Table 8.28.

Table 8.27: Request simulation (S....x)

Column Example value Description

0-1 S, Initiation of Sx command.

2-11 0000000360 Simulated counts.

12 , Separation character (can be anything except x).

13-22 0000000360 Simulated Frequency in Hz

23 , Separation character (can be anything except x).

24-33 00244 Simulated Temperature ADC value. See Equation 8.1 .

34 x Terminating character.

(8.1)

(8.2)

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8 Commands and responses

An example command is:

S,0000000360,0000000360,0000000360x

0123456789 123456789 123456789 1234

Table 8.28: Response of setting simulation values (S...x)

Column Example value Description

0-1 S, Conﬁrmation of S...x command.

2-13 0000094000c, Simulated counts.

14-25 0000000000f, Simulated frequency in Hz.

26-37 0000000245t, Simulated temperature ADC value. See Equation 8.1 .

38-39 r, Beginning of calculated readings.

40-47 18.04m, Calculated

48-60 0000000000Hz, Frequency used for calculation.

61-72 0000094000c, Counts used for calculation.

73-85 0000000.204s, Calculated period from counts.

86-92 029.0C Temperature used for calculation.

93-94 Carriage return (0x0d), Line feed (0x0a).

mag

arcsec

An example response is:

S,0000094000c,0000000000f,0000000245t,r, 18.04m,0000000000Hz,0000094000c,0000000.204s, 029.0C

0123456789 123456789 123456789 123456789 123456789 123456789 123456789 123456789 123456789 1234

56 Unihedron SQM-LU Operator’s Manual - 20170728

9 Installation

9.1 Mechanical installation

Unihedron sells an enclosure that is suitable for mounting either the SQM-LE, SQM-LU, SQM-LR, SQM-LU-DL into. You can read more about it, including plans to build your own at www.unihedron.com/projects/sqmhousing/ .

Figure 9.1: Housing

9.1.1 Cover selection

If the unit is to be mounted in exposed location, we recommend the Unihedron plastic weatherproof housing with glass window plate, or an acrylic dome. Acrylic domes will last 2-3 years but eventually weather on the surface. It is not clear that this will aﬀect the reading much. The best test would be to swap a weathered and new one back and forth when changing one out. Presumably the main consideration would be to keep the domes clean every so often and to make sure that the mounting plane is painted black to that it doesn’t reﬂect light back to the inside of the dome and then back into the meter.

Source of scrylic domes: www.globalplastics.ca/domes.htm

9.1.2 Cover calibration

Since the meter is not weather-proof, it must be protected in some way from the elements. The Unihedron meter housing or a plastic dome is recommended. This will reduce the incoming light (approximately 15-20%).

Because a covering will reduce the incoming light, the resultant reading will be darker (higher determined by a simple light experiment should be subtracted from the reading.

Apply this subtraction oﬀset as a negative value, i.e. if you measured 16.60 outside the covering, then 16.75 under the dome, then an oﬀset of -0.15 should be applied to all readings.

An example using the UDM software; if your oﬀset is -0.12 and your factory calibrated light calibration oﬀset is 19.92 then you should change the light-calibration-oﬀset on the calibration-tab to 19.80. European users will see and use a comma instead of a decimal point.

mag

arcsec

value). The oﬀset

9 Installation

Figure 9.2: Example cover calibration

9.1.3 Cover maintenance

Keep the covering clean of dust, water, ice, and bird droppings.

58 Unihedron SQM-LU Operator’s Manual - 20170728

10 Default settings

The SQM-LU contains an FTDI USB interface module.

The FTDI interface has not been altered from its default. There should be no reason to alter the FTDI chip settings. The baud rate is deﬁned by the VCP driver side when a terminal program connects to the SQM-LU.

11 Firmware upgrade

See the UDM “Firmware tab” section on page 34 for instructions on updating the ﬁrmware in the SQM-LU.

11.1 Details

The SQM-LU contains a micro-controller that is equipped with a boot-loader mechanism which is enabled for a few seconds after reboot/reset.

Intel hex strings sent to the unit are used to overwrite program memory. The following link contains a thorough description of the Intel Hex format: http://en.wikipedia.org/wiki/.hex

The basic requirements for ﬁrmware uploading are:

1. Reset micro-controller by sending the hex character 0x19

2. Within a few seconds, send the ﬁrst Intel hex record. The colon “:” character indicates the beginning of an Intel Hex record.

3. Wait for a response of “Ok” followed by “CR LF” which indicates that the record was processed properly.

4. Continue sending records and waiting for the acknowledgement.

5. The unit will reset on its own when no more records have been sent for a few seconds.

12 Calibration

The SQM-LU is factory calibrated and a sheet of the calibration values was provided with the unit. Contact Unihedron with your unit’s USB S/N if you need a copy of the original calibration sheet.

Some possible reasons for recalibration are:

1. A new covering/housing is being used besides the small case that the unit was shipped with.

2. A regular maintenance program is desired. There is no great need for this as the SQM-LU has no analog components.

3. Compensation for aged housing, if a plastic dome is used that might have degraded over time.

4. Replaced lens or changed ﬁeld of view for experimental reasons.

12.1 Recalibration

There is no easy way to perform in-ﬁeld recalibration. It is recommended to send the unit back to Unihedron for proper calibration. There is a nominal fee for recalibration and shipping. Please contact Unihedron for details.

12.2 Light calibration

The sensor must have a reference point for an amount of light against the signal produced. It is not recommended that this be done after factory calibration and relied upon since an improper setup will result in non-standard results.

A ﬂuorescent light or green LED is used to simulate the spectrum that the meter would see during the night sky. A light meter is used to adjust the light reading to 13.5 fc at the place of the SQM-LU. The light calibration routine inside the SQM-LU expects to see this value.

The light that the SQM-LU and light meter see must be coming from an evenly lit surface.

The “light calibration” command can be sent to the unlocked SQM-LU to set the calibration value.

12.3 Dark calibration

The optical sensor in the SQM-LU produces a reading even when totally dark. This “dark level” reading must be determined so that the meter can compensate for it.

The method of dark calibration is simply to prevent any light from entering the meter then execute a “dark calibration” command to the unit. A darkroom bag is one way to prevent light from entering the unit.

The optical sensor provides timed pulses depending on the amount of light entering. In a dark environment the pulses will be long. The meter has a timeout of 300 seconds, so the dark calibration will take at least 5 minutes (300 seconds) to perform.

Place the unit in a dark environment and monitor the timed readings (rx reading request) until they are consistent, normally the value is in the 80-300 second range, then execute the “dark calibration” command.

12.4 Conﬁrmation

Once the calibration has been done, you should be able to get a light reading from the unit at the calibration light level of the same value as the value printed on your calibration sheet in the “Calibration oﬀset” ﬁeld, Normally this ﬁeld has a value of 8.71 mags/arcsec2.

13 Troubleshooting

Table 13.1: Reading seem too bright

Problem The meter reads values that are brighter than expected.

Cause The IR ﬁlter may have fallen out of the lens.

Solution Ensure that there are no extra sources of visible light in the ﬁeld of view of the meter.

Inspect lens for IR ﬁlter. You should see a light blue colour inside the lens.

Table 13.2: Reading is 0.00mpsas

Problem The meter reads values of 0mpsas.

Cause In bright light over about 6mpsas (even indoors) the meter saturates and will produce a reading

of 0mpsas.

Solution Test the meter in a darker setting or place a cover over the meter while doing indoor testing.

Note: in complete darkness (like a photo-darkroom), the meter may timeout and also produce strange readings.

Table 13.3: Cannot Find UDM software

Problem Microsoft Edge cannot ﬁnd UDM software on the CD. Error “Can’t reach this page”.

Cause Microsoft Edge has protections in place to hide ﬁle lists on remote drives.

Solution Use the File Manager to navigate the CD to the Windows directory then install from there. Or,

get the latest Windows version of UDM from the Unihedron website: unihedron.com/projects/darksky/cd/Windows/

Table 13.4: Driver not found

Problem USB driver not found

Cause Some operating systems may not have the FTDI VCP USB driver installed by default.

Solution You can get the most updated driver for your operating system from FTDIchip.com here: http:

//ftdichip.com/Drivers/VCP.htm

Table 13.5: USB device not found, or more than one device on the same COM port

Problem USB device not found, or more than one device on the same COM port

Cause Faulty USB driver

Table continued on next page ...

Table 13.5 – continued from previous page

Solution Ensure that the latest FTDI USB VCP driver is installed, you can check the version number from

FTDIchip.com here: http://ftdichip.com/Drivers/VCP.htm

Use the UDM software to identify found devices. The SQM-LU device has a serial number preﬁx

of FT...... This may help identify what the other device is.

Remove any other USB devices attached to the system to troubleshoot this problem.

Try to reassign the SQM-LU to another COM port using the Windows Device Manager. For example, it the SQM-LU is assigned to COM1, then try to assign it to a free COM port number.

Table 13.6: Recording stops

Problem The meter stops recording while connected to the computer

Cause Some computers, especially laptops, have the “USB suspend mode” activated which puts the USB

port to sleep when there is not enough activity on the computer.

Solution The USB sleep issue can be corrected by ensuring that your power settings do not put the USB

ports to sleep when the computer is inactive. This can be true for any operating system. In Windows, the Windows Control panel procedure to disable the USB suspend setting is located here:

Start Control Panel Hardware and Sound Power Options Edit Power Plan Settings

Put the computer to sleep while plugged in = Never Change advanced power settings USB Settings USB selective suspend setting Plugged in = Disabled OK Save changes

Table 13.7: Meter cannot be found by PC

Problem Meter cannot be found, or stops working intermittently when connected to computer.

Cause Faulty FTDI USB module inside meter.

Table continued on next page ...

Unihedron SQM-LU Operator’s Manual - 20170728 63

13 Troubleshooting

Table 13.7 – continued from previous page

Solution There is not much that can be done to correct this aside from replacement. However, the following

test usually reliably proves the issue. While connected to the computer using UDM, run the unit in “Log continuous” mode at 1 second sampling for at least 1000 samples. If there are any missed readings, the “records missed” counter on the screen will increment and show Red. The test procedure is as follows:

1. Start UDM and select the device.

2. Press the “Reading” button to test connectivity.

3. Press the “Log continuous” button.

4. Select “Every x seconds”.

5. Enter 1 into the s box to the right of the selection.

6. Press “Record”.

7. Let this run for at least 1000 records and watch that are no “Records missed”.

Table 13.8: Meter cannot be found by Windows operating system

Problem The windows computer cannot identify the SQM-LU, and re-installing the FTDI device drivers

does not help.

Cause The Windows FTDI driver installation may be storing old attempts at installing drivers that should

have been cleared out.

Solution The following steps can be used to clean up the FTDI entries in Windows:

1. Install this FTDI “CDM Uninstaller” utility at: www.ftdichip.com/Support/Utilities/CDMUninstaller v1.4.zip

2. The detailed instructions for its operation are here: www.ftdichip.com/Support/Utilities/CDM Uninst GUI Readme.html

3. Here is a quick summary of the instructions:

4. Start up the CDM uninstaller program

5. Press - Add

6. Press - Remove devices

7. Wait 5 minutes or so until complete

8. Close

9. Re-insert SQM-LU device

10. Wait 5 minutes or so for Windows to install driver and port

64 Unihedron SQM-LU Operator’s Manual - 20170728

Table 13.9: Cannot get a reading

Problem Cannot get a reading

Cause Driver is not installed or the SQM-LU is not connected

Solution For Windows, check that the unit is registered using the registry editor from the Start menu, select

Run, then type in regedit and press OK. For Windows XP and Windows 2000, look here for your device

HKEY LOCAL MACHINE\

SYSTEM\

Enum\

FTDIBUS\

VID 0403+PID 6001+Serial Number\

0000\

PortName

For Windows 98 and Windows ME, look here for your device

HKEY

LOCAL MACHINE\

SYSTEM\

Enum\

FTDIBUS\

VID 0403+PID 6001+Serial Number\

0000\

PortName

The Serial Number is printed on the bottom of the unit. The above will identify which COM port the SQM-LU has been assigned. If the SQM-LU is plugged in, the active COM port will show up in this list:

HK LOCAL MACHINE\

HARDWARE\

DEVICEMAP\

SERIALCOMM

For Linux and Mac, use lshal to determine which device the FTDI driver has attached the SQMLU to. The CD contains a Perl script findftdi.pl to ﬁlter out the lshal output.

Unihedron SQM-LU Operator’s Manual - 20170728 65

14 Glossary

Table 14.1: Glossary of terms

ADC Analog to Digital Converter. A device usde to convert an analog signal into a digital value.

CCD Charge coupled device is a type if image sensor.

EEPROM Electrically Erasable Programmable Read Only Memory is a type of memory that retains its

contents after the power has been removed. This type of memory has a limited write/erase cycle as well as a lifetime for data retention. In the SQM-LU, the parameters in the micro-controller can be written 1 million times and last for 100 years.

Firmware The program that resides inside the device. In the case of the Unihedron SQM products, it is

the software runs the device including reading and reporting the light values.

FITS Flexible Image Transport System is an open standard deﬁning a digital ﬁle format useful for

storage, transmission and processing of scientiﬁc and other images.

FTDI Future Technology Devices International is the manufacturer of the USB module inside the

SQM-LU. FTDI also supplies the VCP software driver for the computer operating system so that the SQM-LU can communicate with the computer.

GPS Global Positioning System. A GPS receiver may be connected to a computer to allow UDM to

integrate the location information into the logged data. See UDM for mode details.

mpsas Magnitudes per square arcsecond. The unit of measurement reported by the SQM.

NMEA National Marine Electronics Association data format that the GPS receiver produces.

RAM Random Access Memory. Temporary memory that only retains data while power is applied.

SQM-LU Sky Quality Meter with Lens and USB connectivity,

UDM Unihedron Device Manager is software used to access the SQM series of meters.

USB Universal Serial Bus

VCP Virtual COM port (VCP) drivers cause the USB device to appear as an additional COM port

available to the PC. Application software can access the USB device in the same way as it would access a standard COM port. The SQM-LU requires the FTDI VCP driver be installed on the computer operating system so that communications can be done with the meter.

15 Bibliography

[1] Christopher Kyba, etc., Worldwide variations in artiﬁcial skyglow. PNAS, Volume 1, Issue 6, 2014.

[2] Wikipedia, Apparent Magnitudes of Known Celestial Objects. http://en.wikipedia.org/wiki/Apparent_magnitude

[3] Schaefer, B.E. Feb. 1990. Telescopic Limiting Magnitude. PASP 102:212-229 http://adsbit.harvard.edu/cgi-bin/

nph-iarticle_query?bibcode=1990PASP..102..212S

[4] Olof Carlin, Nils. About Bradley E. Schaefer, Telescopic limiting Magnitudes, Web page discussion of brightness

in Schaefer (1990) and Clark (1994). http://w1.411.telia.com/~u41105032/visual/Schaefer.htm(accessed7/

2003)

[5] NELM Converter, K. Fisher ﬁsherka@csolutions.net Rev. 8/2006 http://unihedron.com/projects/darksky/

NELM2BCalc.html

H¨orstemeier Version 2.0 2001-07-07 Algorithms taken from the book ”Astronomical Algorithms” by Jean Meeus

Unihedron SQM-LU, SQM-LU-DL-V Operator's Manual

Specifications and Main Features

Frequently Asked Questions

User Manual

List of Figures

List of Tables

1 Introduction

2 Measurements

3 Theory of operation

5 Hardware connections

6 Software development

7 Unihedron Device Manager

\Windows\setup1.0.0.38.exe

8 Commands and responses

8.6.3 Interval setting response

9 Installation

10 Default settings

11 Firmware upgrade

12 Calibration

13 Troubleshooting

14 Glossary

15 Bibliography